1. Field of the Invention
This invention generally relates to a chemically amplified positive resist composition which is highly sensitive to actinic radiation such as deep-UV, electron beam and X-ray, can be developed with alkaline aqueous solution to form a pattern, and is thus suitable for use in a fine patterning technique. More particularly, it relates to a bisphenol carboxylic acid tertiary ester derivative which is useful as a dissolution inhibitor in such chemically amplified positive resist compositions.
2. Prior Art
As the LSI technology tends toward higher integration and higher speed, further refinement of pattern rules is required. The current patterning technology mostly relies on light exposure which is now approaching the essential limit of resolution which is dictated by the wavelength of a light source. It is generally recognized that in light exposure using g-line (wavelength 436 nm) or i-line (wavelength 365 nm) as a light source, a pattern rule of about 0.5 .mu.m is the limit. For LSIs fabricated by such light exposure technique, a degree of integration equivalent to 16 mega-bit DRAM is the limit. At present, LSIs fabricated in the laboratory have reached this stage. It is urgently required to develop a finer patterning technique.
Under such circumstances, deep-ultraviolet lithography is regarded promising as the next generation of fine patterning technology. The deep-UV lithography is capable of working on the order of 0.3 or 0.4 .mu.m. If a less light absorbing resist is used, it is possible to form a pattern having a side wall nearly perpendicular to the substrate. Attention is now paid to the technique of utilizing a high illuminance KrF excimer laser as a light source for deep-UV. In order that an excimer laser be utilized in mass-scale manufacture, a resist material featuring low light absorption and high sensitivity is desired.
Chemically amplified, positive working resist materials using acid catalysts were recently developed as disclosed in JP-B 27660/1990, JP-A 27829/1988, U.S. Pat. No. 4,491,628 and No. 5,310,619. These materials have high sensitivity, resolution and dry etching resistance and are promising as resist materials especially suited for deep-UV lithography.
With respect to the chemically amplified positive resist materials, it is known that their function is largely governed by the dissolution inhibitor used. One typical example of the known dissolution inhibitors is given below. ##STR1##
This compound itself is an oil soluble compound. When it is blended as one component of resist material, it serves for three functions of reducing the solubility of the resist material in aqueous base, suppressing film thinning upon development, and in exposed areas, releasing an acid-labile group in the presence of an acid generated so that the resist material becomes soluble in an alkaline developer to increase the dissolution rate of exposed areas.
Chemically amplified positive resist materials using the above-specified compound as a dissolution inhibitor, however, fail to provide high resolution upon alkaline development and undergo profile deterioration due to scum generation. The following two facts account for these drawbacks.
First, decomposition of an acid-labile group is insufficient even after exposure. In the above-specified compound, the acid-labile group which protects phenol is a tert-butoxycarbonyl group. Since this protective group has relatively low acid lability, acid decomposition can be insufficient even after exposure when the above-specified compound is combined with particular resist components.
Secondly, the difference in alkali dissolution rate between the above-specified compound and its acid decomposed product is not so significant. It is noted that the ratio of alkali dissolution rate of the latter to the former is referred to as a dissolution contrast. Since the acid decomposed product of the above-specified compound is a phenol derivative, its increase of dissolution rate in aqueous base is insufficient as compared with carboxylic acid derivatives.
JP-A 167811/1994 discloses a dissolution inhibitor of a similar structure to formula (1) to be defined below in which the hydrogen atom of carboxylic acid is replaced by an alkoxyalkyl, cyclic ether, vinyloxyalkyl or tert-alkoxycarbonylalkyl group. This dissolution inhibitor, however, is unstable in resist material in the presence of a phenolic alkali-soluble resin (that is, under faintly acidic conditions).